Following the tutorial I cannot move further after installing text editor
and inserting the command

vi /etc/network/interfaces

in order to change DHCP into static.
How do I move further and get out of this network configuration window?
"/etc/init.d/networking restart" didn't work:

"Point 7 Configure The Network
Because the Ubuntu installer has configured our system to get its network settings via DHCP, we have to change that now because a server should have a static IP address. Edit /etc/network/interfaces and adjust it to your needs (in this example setup I will use the IP address 192.168.0.100):

vi /etc/network/interfaces

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).